The Japanese army defending Manchuria when the Soviet invasion began was called the Kwantung Army.
The Soviet invasion of Manchuria began on August 9, 1945, against Japanese-occupied Manchuria and the puppet state of Manchukuo. The Kwantung Army was the principal Japanese formation in the region, although Japanese forces also included units in Korea and other areas.
Once considered an elite Japanese force, the Kwantung Army had been weakened by transfers of experienced troops to other fronts. The Soviet attack used large mechanized formations and advanced across multiple directions, rapidly overwhelming Japanese defenses in many sectors.
The invasion occurred between the atomic bombings of Hiroshima and Nagasaki. Its impact on Japanese leaders remains part of the historical debate about why Japan surrendered, alongside the atomic attacks and the worsening military situation.